Re: [PATCH] qemu: add pointer check in qemuMonitorLastError

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On 9/19/19 10:01 AM, Xu Yandong wrote:
We found a exception when libvirt occurrs segmentation fault.
thread 1 is waiting object lock in qemuConnectMonitor,
qemu process exits and sends EOF event as well, so thread 2 invokes
qemuMonitorLastError but pointer mon is NULL.

Signed-off-by: Xu Yandong <xuyandong2@xxxxxxxxxx>
---
  src/qemu/qemu_monitor.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index aa230b3306..28f18391a5 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -1103,7 +1103,7 @@ qemuMonitorSend(qemuMonitorPtr mon,
  virErrorPtr
  qemuMonitorLastError(qemuMonitorPtr mon)
  {
-    if (mon->lastError.code == VIR_ERR_OK)
+    if (!mon || mon->lastError.code == VIR_ERR_OK)
          return NULL;
return virErrorCopyNew(&mon->lastError);


This works, but I think we need a better approach. The problem is, we register monitor FD into our event loop with unlocked @vm and only after that we try to lock @vm back and set priv->mon = mon (this is all done in qemuConnectMonitor()). I have better fix in mind but I have to run now, will post it tomorrow, if that's okay with you.

Michal

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